If $x \star y = x(y-5)$ and $x \triangleright y = 2x-6y$, find $(6 \triangleright 0) \star 6$.
First, find $6 \triangleright 0$ $ 6 \triangleright 0 = (2)(6)-(6)(0)$ $ \hphantom{6 \triangleright 0} = 12$ Now, find $12 \star 6$ $ 12 \star 6 = 12(6-5)$ $ \hphantom{12 \star 6} = 12$.